Systems are knwon for determining the position or location of an object within a defined area. Such systems find utility for the entry of graphic and other information into a computer, and are often embodied into a data entry tablet which includes means for sensing the position of a stylus or other point movable within a defined area, and for providing an electrical signal which is representative of successive stylus positions, thereby to denote lines, curves and figures drawn by the stylus on the tablet. Another known use for position determining systems is for land surveying and wherein means are provided for sensing the position of a target movable within a defined area, and for providing a signal representative of the sensed target positions and from which survey information can be derived.
A related data entry device is known as a cursor controller or "mouse", which is usually in the form of a small housing movable over a surface and which provides corresponding movement of a cursor on a display screen. Movement of the cursor can be employed for data entry of graphical information and can also be used as a pointer for identifying a position on the screen or information displayed on the screen, such as for interactive computer usage. In general, mouse movement is provided by a ball that rolls over a surface, the ball movement being sensed by mechanical or optical means. Motion can also be sensed via a specially prepared sensible surface over which the mouse is moved. For example, a checkerboard pattern has been employed on a surface, and light reflected from the surface is detected by a photodetector which provides pulse signals indicative of motion with respect to the surface pattern. A review of several different types of mouse cursor controllers is provided in an article entitled "Interfacing Mice to Computers", Machine Design, Jan. 12, 1984, pp. 84-91.
Graphic input devices are known using pairs of scanned light beams, as shown, for example, in U.S. Pat. Nos. 3,553,680; 3,613,066; 3,364,389; and 4,294,543. In this type of entry device, first and second narrow light beams are scanned across a surface and means are provided for sensing the light beams at intersecting points within a surface, the angular position of the two beams at the detected intersections representing the position within the defined area. Another known technique employs orthogonal light beams provided across a display surface, the interruption of selected orthogonal pairs of beams providing an identification of the data entry point.
Examples of surveying and related systems for automatic position determination are shown in U.S. Pat. Nos. 3,714,657; 3,400,398; 3,437,825; and 3,443,095. Range measuring systems are shown for example in U.S. Pat. Nos. 2,830,487; 3,759,614; and 3,961,851.